Intravenous Calcitriol Therapy Increases Serum Concentrations of Fibroblast Growth Factor-23 in Dialysis Patients with Secondary Hyperparathyroidism

BACKGROUND/AIMS: Fibroblast growth factor-23 (FGF-23) is a recently discovered phosphaturic factor. Although increased levels of serum FGF-23 have been reported in dialysis patients, the role of high FGF-23 levels remains unclear. Since FGF-23 is associated also with vitamin D metabolism, we examined the changes of serum FGF-23 levels in chronic dialysis patients treated with intravenous calcitriol therapy. METHODS: Thirty patients with severe secondary hyperparathyroidism were treated with intravenous calcitriol (0.5-1.0 microg) two or three times per week for 6 months. The changes of serum levels of calcium, phosphate, intact PTH, and FGF-23 were evaluated. RESULTS: Baseline serum FGF-23 levels were markedly high. By intravenous calcitriol therapy, intact PTH levels decreased effectively in the first month (p < 0.001). In contrast, FGF-23 levels increased gradually during the study period (p = 0.027). The Delta serum FGF-23 level was significantly correlated with the total doses of calcitriol injected intravenously in 6 months in patients with refractory secondary hyperparathyroidism (R2 = 0.147; p = 0.036). CONCLUSIONS: Intravenous calcitriol decreased serum intact PTH level and increased serum FGF-23 levels significantly. Extremely high levels of serum FGF-23 in these patients may be attributed, at least in part, to the cumulative dose of vitamin D.